Hitherto, a repair of a leak in a pipe or pipeline carrying fluid at low pressures, typically up to 2 PSI (140 mbar), or what is termed the semi-medium pressure range up to 10 PSI (700 mbar) have been repaired by using a flexible muff wrapped and secured around the pipe or pipeline, sealant material being introduced into the space between the muff and the pipe or pipeline. For pressures higher than the semi-medium pressure range, a rigid mould has been required since the flexible muff arrangement is not capable of withstanding the higher pressures. Use of a rigid mould involves the expense of the mould itself and, since the mould is designed to be reusable, it is often difficult to judge when the sealant has set so that the mould can be released. Release of the mould too early would mean that the repair could be unsatisfactory.